In both elective surgery and emergency medical situations, it is often necessary for medical personnel to secure the airway of the patient through a procedure known as endotracheal intubation. Intubation requires the intubator to insert a tube, either through the mouth or nose, into the trachea of the patient. The tube permits active monitoring and proactive control of the patient's breathing and additionally permits the direct administration of anesthesia or other drugs.
Potential damage to the vocal cords and the danger of esophageal placement (rather than tracheal placement) of the tube dictate that intubation be performed by a skilled professional. However, even an experienced intubator occasionally encounters a patient who has what is commonly referred to as a "difficult" airway.
Patients whose tracheas are difficult to intubate have been well known in the anesthesia community for decades. Intubating difficulties are especially prevalent among those who have: problems with obesity or have short, thick necks or short mandibles; cervical arthritis, temporomandibular joint problems, or previous cervical fusions; fractures of the mandible, maxilla, or cervical spine; tumors or abscesses in the mouth, pharynx or neck; suffered trauma to the face or neck; and those having congenital syndromes.
The American Society of Anesthesiologists has studied respiratory injuries suffered by patients with difficult airways. This study determined that the occurrence of injuries related to difficult intubation is not improving. In the 1970s, for example, such injuries accounted for 5% of malpractice claims that resulted in death or brain damage. In the 1990s, that figure has increased to 12%.
Current devices used for intubating a difficult airway vary depending on the particular situation. For example, in an unhurried elective situation (as before routine surgery), a patient that requires intubation is usually approached with one of several types of fiberoptic scopes. Fiberoptic scopes are popular for elective procedures largely due to their safety record. Since the procedure is elective and not an emergency, an unhurried, careful approach to intubation is possible. Furthermore, failure of fiberoptic intubation typically does not harm the patient.
Unfortunately, fiberoptic scopes are ineffective under certain circumstances. In particular, fiberoptic failure rates are high where there is distortion of the anatomy. For example, fiberoptic failure may occur in the presence of a tumor or abscess or where there is a greatly increased amount of soft tissue present in the upper airway, as is common with morbid obesity. Furthermore, due to their reliance on optics, fiberoptic scopes are difficult to use when blood or excess secretions are present in the airway. In addition to these drawbacks, fiberoptic scopes are generally perceived to be expensive and relatively fragile.
When fiberoptic techniques fail, the alternatives are much more painful and traumatic for the patient and more difficult for the intubator. One option is the insertion of a retrograde wire. This technique involves piercing the larynx just below the vocal cords with a hollow needle and threading a wire upwardly between the vocal cords and into the mouth. An intubation tube may be slid over the wire and into place. Alternatively, a fiberoptic scope having a wire receiving guide may be placed over the wire. Regardless, retrograde wire techniques involve trauma to the larynx that may cause airway bleeding or hematoma. In addition, finding the larynx and placing the wire may be difficult in an obese patient. Furthermore, even if the wire is properly placed, there is a very short distance between the vocal cords and the exit of the wire from the larynx (i.e., the wire will exit the larynx through the neck immediately below the vocal cords). Thus, whatever device is threaded over the wire may easily become dislodged from the glottis when the wire is removed.
Intubators sometimes utilize a lighted stylet having a light source visible outside the neck of the patient. Lighted stylet techniques, however, have the disadvantage of working best in a dark environment. Additionally, they do not work well in patients with thick necks.
Another option is to proceed with the induction of anesthesia and attempt direct laryngoscopy. Direct laryngoscopy involves anesthetizing the patient and inserting a rigid laryngoscope into the mouth to examine the larynx. Unfortunately, such a procedure involves substantial risks. Apnea from the induction agent and paralysis from muscle relaxants can be life-threatening. With even the shortest acting paralytic (succinylcholine), 8-10 minutes is required to reestablish spontaneous ventilation.
Yet another option is to use a laryngeal mask airway (LMA). An LMA is a tube-like device with a oval cup at the distal end designed to form a low pressure seal between the LMA tube and the glottis without insertion into the larynx. Unfortunately, LMAs and other supraglottic devices (e.g., combitude), while appropriate for some types of surgery, are contraindicated in patients who are at risk for regurgitation or esophageal reflux since these devices do not protect the airway from stomach contents.
In addition to elective surgery, difficult intubations are also prevalent in the emergency room (ER). Emergency intubations are generally much more challenging for various reasons. For instance, because blood and excessive secretions in the mouth and/or airway are common, fiberoptic techniques are used less frequently in the ER. Additionally, patients typically are not as cooperative as those undergoing elective procedures. Furthermore, there is often concern about cervical spine injuries that make movement of the neck potentially injurious.
As discussed with respect to elective procedures, direct laryngoscopy with or without drugs is available in the ER. Unfortunately, this procedure poses risk of injury to patients who have suffered cervical spine damage even if manual cervical stabilization is first administered. Direct laryngoscopy with induction agents or paralytics may furthermore cause loss of patency of the airway and aspiration of the stomach contents.
Another option in the ER involves blind nasal techniques. While advantageous in some circumstances, such techniques are potentially dangerous where basilar skull fracture is present. Furthermore, these techniques are known to have a high failure rate.
Some practitioners recommend that the intubator place an ear near the proximal end of the endotracheal tube as it approaches the glottis. Breathing sounds may then be used to indicate the tube position relative to the glottis. Such a technique has drawbacks though. First, coughing by the patient may propel blood and mucus through the tube into the operator's ear or face. Second, the intubator is poorly oriented to observe other aspects of the procedure such as head and neck position, patient response to maneuvers, and vital sign monitors such as pulse oximetry and EKG. Finally, depending on the patient's injuries and the ambient noise in the room, the intubator may be unable to detect any sounds. For these reasons, listening devices for use with endotracheal tubes have been described generally for use after tube insertion for the monitoring of vital signs and sounds.
Other methods are known that provide an external energy source and attempt to locate the trachea based on reflected energy readings. While effective in most circumstances, these devices are complex, requiring an energy source and wave form energy transmitter. As such, these devices are bulky and relatively expensive and are not widely used.
Thus, there are unresolved issues with current devices used for intubating difficult airways in spontaneously breathing patients. Particularly, current devices are expensive and are difficult to use in the presence of anatomical abnormalities (e.g., soft tissues mass, abscess) or blood or secretions in the airway. What is needed is a simple intubating device that is safe to use, inexpensive, and effective in a broad range of circumstances.